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Randomized comparison of laryngeal tube with classic laryngeal mask airway for anaesthesia with controlled ventilation
British Journal of Anaesthesia 91 (3): 373±8 (2003)
DOI: 10.1093/bja/aeg192
Randomized comparison of laryngeal tube with classic laryngeal mask airway for anaesthesia with controlled ventilation T. M. Cook1*³, B. McCormick1 and T. Asai2 1
Royal United Hospital, Combe Park, Bath, UK. 2Assistant Professor, Kansai Medical University, 10±15 Fumizono-cho, Moriguchi City, Osaka 570±8507, Japan *Corresponding author
Methods. We randomly allocated 72 patients to receive either the laryngeal tube or an LMA, and compared adequacy of controlled ventilation during anaesthesia (good: clear airway without complications; fair; clear airway with complications or suboptimal airway; or failed), leak pressure and the incidence of postoperative complications. Results. Insertion was successful within 2 attempts in all 36 patients for the classic LMA and in 35 patients for the laryngeal tube. The mean leak pressure for the laryngeal tube (28 cm H2O) was signi®cantly greater than that for the classic LMA (21 cm H2O) (P<0.001; 95% CI 3.6±10.0 cm H2O). Ventilation was good in 25 cases, fair in 11, and failed in no patients with the classic laryngeal mask airway; and good in 23, fair in 11 and failed in two for the laryngeal tube. There was no signi®cant difference in adequacy of ventilation between the groups. The median peak airway pressure for the laryngeal tube (17.5 cm H2O) was greater than that for the classic LMA (16 cm H2O) (difference: 2 cm H2O; 95% CI 0±5 cm H2O). There was no signi®cant difference in the incidence and severity of the postoperative complications between the two groups. Conclusion. The laryngeal tube was as effective as the classic LMA during anaesthesia with controlled ventilation. There were similar operative and postoperative complications. Br J Anaesth 2003; 91: 373±8 Keywords: equipment, masks laryngeal; equipment, tubes laryngeal Accepted for publication: April 3, 2003
The laryngeal tube (VBM, Medizintechnik, Sulz, Germany) has been developed to secure a patent airway during either spontaneous breathing or controlled ventilation. It consists of an airway tube with a small balloon cuff attached at the tip (distal cuff), and a larger asymmetric balloon cuff at the middle part of the tube (proximal cuff; Fig. 1). The cuffs are in¯ated through a single pilot tube and balloon, through which cuff pressure can be monitored. There are two distal apertures in the tube between the two cuffs through which gas movement may take place. When the device is inserted, it lies along the length of the tongue and the distal tip is positioned in the hypopharynx. The proximal cuff provides a seal in the upper pharynx and the distal cuff seals the oesophageal inlet. There are three black lines on the tube near a standard 15-mm connector, which indicate adequate
depth of insertion when aligned with the teeth. The device is made of silicone and is re-usable, after sterilization in an autoclave, up to 50 times. There are ®ve sizes, suitable for neonates up to large adults. Since its introduction into clinical practice, the design of the laryngeal tube has been modi®ed on a few occasions: the prototype had two pilot tubes whereas the current device has one; a softer silicone has been used for the tip of the device (in the distal cuff) to reduce oropharyngeal injury; the distal aperture consists of two ori®ces (instead of one in the prototype); there is an indentation of the proximal cuff ²
LMAâ is the property of Intavent Limited. Declaration of interest. Dr Cook has received an honorarium from Intavent Limited. ³
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2003
Downloaded from http://bja.oxfordjournals.org/ at State Univ NY at Stony Brook on October 30, 2014
Background. Only a prototype laryngeal tube has been compared with the classic LMA² for brief periods of anaesthesia. We compared the new laryngeal tube (which had several improvements in design) with the classic LMA.
Cook et al.
Standard anaesthesia monitors were attached before induction of anaesthesia. The patient's head was supported on a ®rm pillow. After preoxygenation, anaesthesia was induced with a target controlled infusion of i.v. propofol set to give a predicted plasma concentration of 4±7 mg ml±1, and fentanyl 1 mg kg±1. Neuromuscular block was with rocuronium 0.6±1.0 mg kg±1, con®rmed using a peripheral nerve stimulator (train-of-four count=0) before airway manipulation. Anaesthesia was maintained with a targetcontrolled infusion of propofol. The patients were then allocated randomly to one of two groups, in which the laryngeal tube or the classic LMA was speci®ed for airway management. Randomization was by 72 sequentially numbered, sealed opaque envelopes containing equal numbers of the names of either of the two devices.
around the second distal ori®ce, and two side holes are added near the distal ori®ce. The laryngeal tube can be used as an alternative to the classic LMA during maintenance of anaesthesia. There have been three studies comparing the ef®cacy of the laryngeal tube with the classic LMA.1±3 One study showed that the success rates of insertion was similar in the two groups, and the laryngeal tube provided a better seal than the classic LMA.1 In a second study,2 arterial blood gas analysis obtained 10 min after insertion of the test device showed that the laryngeal tube was as effective as the classic LMA. However, in the third report,3 the study was stopped because of a high failure rate with the laryngeal tube. In all studies, prototype laryngeal tubes were used. There has been no study comparing the current type of the laryngeal tube with other airway devices, such as the classic LMA, and no studies comparing these two devices during the entire course of anaesthesia. Our aim was to compare the ef®cacy of the laryngeal tube with that of the classic LMA in paralysed patients during the entire course of anaesthesia, and to compare the sealing effects of the two devices.
Methods The local research ethics committee approved the study and all patients gave written informed consent. We studied 72 adult patients (ASA I or II) undergoing elective surgery in the supine or lithotomy position, in whom neuromuscular block was part of the anaesthetic technique and the use of the classic LMA was appropriate. Patients were excluded if they had any diseases of the neck, upper respiratory or upper alimentary tract, or if they were at risk of pulmonary aspiration of gastric contents. The view of the oropharynx at opening the mouth was scored according to Mallampati and colleagues4 as modi®ed by Samsoon and Young.5
The laryngeal tube was inserted according to the manufacturer's instructions. Brie¯y, before insertion, cuffs were de¯ated and a water-soluble lubricant (KY jelly) was applied to the cuffs. The patient's head was extended on the neck (`snif®ng position'). The tip of the laryngeal tube was placed against the hard palate behind the upper incisors and the device was slid down into the centre of the mouth until resistance was felt or the second bold black line on the tube had just passed between upper and lower teeth. The cuffs were in¯ated using a cuff in¯ator (VBM, Germany) until the intracuff pressure reached 80±90 cm H2O. The pressure was then reduced to 60±70 cm H2O.6 A size 3 was used for patients less than 155 cm, a size 4 for those between 155 cm and 180 cm, and a size 5 for those >180 cm in height.6 The classic LMA was inserted according to the manufacturer's instruction manual.7 A size 4 was used in females and a size 5 mask for males.8 The back of the cuff was lubricated with KY jelly. The cuff was in¯ated using the same cuff in¯ator until the intracuff pressure reached 60±70 cm H2O.7 In both groups, the breathing system was connected to the device. We assessed adequacy of ventilation by gently squeezing the reservoir bag, observing the presence of endtidal carbon dioxide waveforms and chest movement. If it was not possible to ventilate the lungs, the following airway manoeuvres were allowed: chin lift, jaw thrust, head extension, or ¯exion on the neck. In the case of the laryngeal tube, the position was also allowed to be adjusted by gently pushing or pulling the device (whereas no such manoeuvre was allowed for the classic LMA). After any manoeuvre, adequacy of ventilation was re-assessed. If it was not possible to insert the device or ventilate through it, one more attempt at insertion was allowed. If placement had failed after two attempts, the study was abandoned and the airway maintained either through a classic LMA or such other airway device as suitable. Time for insertion of the airway (from time of picking up the device to attaching it to the breathing system after
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Insertion of the device
Fig 1 The laryngeal tube (VBM, Germany).
Comparison of laryngeal tube with classic LMA
in¯ation of the cuff) was measured in patients in whom it was possible to ventilate the lungs. To measure the seal pressure, fresh gas was insuf¯ated at 5 litre min±1, the spill valve occluded and we recorded the minimum airway pressure at which gas could either be heard leaking around the airway device or the airway pressure plateaued. Peak airway pressure was not allowed to exceed 40 cm H2O.
Maintenance of anaesthesia
Removal of the device At the end of the operation, anaesthetic agents were discontinued while the device was left in place. The device was removed after the patient regained consciousness spontaneously and responded to verbal command to open the mouth. However, if necessary (e.g. airway obstruction or retching occurred), it could be removed before this point. Before removal, the cuffs of the laryngeal tube were de¯ated, whereas the cuff of the classic LMA was not (in accordance with the manufacturers' recommendations7). At removal, the presence or absence of secretions interfering with airway management and of blood on the device was recorded. Complications, were de®ned, a priori, with the use of the devices during induction, maintenance, and emergence.
Postoperative period Within 2 h and again at 24 h after surgery, each patient was questioned to determine the following complications: sore throat (constant pain, independent of swallowing), dysphagia (dif®culty or pain with swallowing), sore jaw, dysphonia (dif®culty or pain with speaking), numbness of the tongue or the oropharynx, blocked or painful ears, reduced hearing, or neck pain. Each complication was graded as: none, mild, moderate or severe. Those patients discharged from hospital within 24 h after surgery were followed-up by telephone.
The primary aim of the study was to compare the success rates of two airway devices in establishing a patent airway allowing ventilation without complications. The secondary aim was to compare the leak pressures between two groups. We calculated the number of patients required for the study based on these two factors. The rate of the classic LMA providing a patent airway is 95±100%.9 Our hypothesis was that there would be no difference in the ef®cacy of the two devices in terms of ventilation during anaesthesia, with a clinically important difference being 10%. Seventy-two patients would be required to assess this hypothesis, with a power of 80% and a one-sided 95% con®dence interval (CI), using an equivalence test.10 The mean airway pressure at which gas leaks around the classic laryngeal mask airway ranges from 18 to 20 cm H2O (SD ~5 cm H2O).11 12 We considered that an increase in leak pressure of 30% would be clinically signi®cant. Twenty-two patients would be required to detect this difference with a power of 80%. Therefore, we studied 72 patients. The c2-test was used to compare the ef®cacies of the two devices: good (optimal ventilation without complications during anaesthesia), fair (optimal ventilation with complications or suboptimal ventilation), and failure (failed insertion or abandonment of the use). Plots of normal scores showed that the data for leak pressures were normally distributed. Therefore, the Student's t-test was used to compare the leak pressures between two groups. For additional information, we also applied the third hypothesis test (c2-test) to compare the incidence of postoperative complications between groups. For this analysis, the number of patients was counted for no, mild, moderate or severe complication. The data for 0±2 h and 24 h after surgery were pooled for analysis and for each patient, with the severest score recorded. P<0.05 was considered signi®cant. We noticed after the start of the study that there might be a difference in the peak airway pressures during anaesthesia between the laryngeal tube and classic LMA. Therefore, the con®dence interval was used to compare this factor. The data for insertion time and for the peak pressure were not normally distributed. Therefore, the 95% CIs were calculated for the median difference of insertion time, the median difference of peak airway pressure, and the mean difference of the leak pressures, between the two devices.
Results Thirty-six patients were studied in each group. Patient characteristics, size of the device used, and duration of anaesthesia, were similar in the two groups (Table 1).
Insertion of the device There was one failure to establish an airway with the laryngeal tube and none with the classic LMA after two
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After securing the device, controlled ventilation in oxygen and air was started with a tidal volume of 7 ml kg±1 and an inspiratory/expiratory ratio of 1:2. The respiratory rate was adjusted to maintain the end-tidal carbon dioxide concentration in the normal range. Ventilation was judged to be optimal if the following four tests were passed: (i) adequate chest movement; (ii) an expired tidal volume of 7 ml kg±1; (iii) stable oxygenation; and (iv) `square wave' capnography. If airway obstruction occurred during anaesthesia, manoeuvring the position of the device or the patient's head and neck, or removal and reinsertion of the device were allowed. The number of manipulations of each device during insertion and maintenance of anaesthesia was recorded for each device.
Statistical analysis
Cook et al.
attempts at insertion (Table 2). Two attempts were required in four patients with the laryngeal tube and in ®ve with the classic LMA. Insertion of the laryngeal tube required manipulations in three patients, but the time taken for insertion was similar for the two groups (Table 2). There were few complications of insertion in either group (Table 3). In the patient in whom insertion of the laryngeal tube failed, there was temporary hypoxia and it was removed. The classic LMA provided a clear airway in this patient.
Maintenance of anaesthesia
Table 1 Patient characteristics, the size of the device used, and duration of anaesthesia. Data are presented as number of patients or mean (SD) for height and weight, mean (range) for age
Sex (M/F) Age (yr) Height (cm) Weight (kg) BMI (kg m±2) View of the oropharynx Mallampati class4 5 1/2/3/4 Size of the device used Size 3/4/5 Duration of anaesthesia (min)
Classic LMA (n=36)
Laryngeal tube (n=36)
21/15 52 (22±84) 171 (10) 78 (14) 27 (4) (21±38)
18/18 56 (22±82) 167 (10) 75 (15) 27 (5) (19±43)
13/18/4/1
15/15/5/1
2/16/18 46 (27) (15±142)
2/30/4 49 (24) (15±120)
Removal of the device The airways were equally well tolerated during emergence from anaesthesia: there was no need to remove the airway before the patient regained consciousness with either device. Complications during emergence and recovery from anaesthesia were few and mostly minor (Table 3). One patient in the classic LMA group developed laryngospasm, stridor and mild desaturation. One patient in the laryngeal tube group developed airway obstruction and mild desaturation. On removal, blood was present on one device in each group (Table 3).
Postoperative period Postoperative complications that could be attributed to the airway device were observed in one-third of patients in each group (Table 3), and there was no signi®cant difference in incidence and severity between the groups.
Discussion We have shown that the laryngeal tube is as effective as the classic LMA at providing a patent airway during controlled ventilation of the lungs, and that the laryngeal tube gave a signi®cantly greater sealing pressure than the classic LMA. The success rate of obtaining a patent airway through the laryngeal tube was high (97%). This result supports previous reports, where the success rate was 94±100% immediately after insertion of the device.1 2 6 13 14 The laryngeal tube provided a patent airway as frequently as the classic LMA, not only during induction of anaesthesia, but also during maintenance of anaesthesia. The airway seal pressure achieved with the laryngeal tube was signi®cantly greater than that with the classic LMA (Table 2), which also supports a previous study.1 2 In this regard, the laryngeal tube may be more useful than the classic LMA for controlled ventilation. The increased seal pressure of the laryngeal tube is achieved with two minor costs: the laryngeal tube required more re-adjustment because of airway obstruction and
Table 2 Success rate of, and time for, insertion of the device, the number of patients in whom manipulation of the device was required to obtain a clear airway, and in whom ventilation was optimal (see details in the text). Data presented as mean (SD) (range) for the leak pressure; median (range) for the insertion time and peak airway pressure
Successful ventilation (1st, 2nd attempt) Time for insertion (s) Manipulations Optimal ventilation Leak pressure (cm H2O) Peak airway pressure (cm H2O)
Classic LMA (n=36)
Laryngeal tube (n=36)
P-value
95% CI
36 15 0 29 21 16
35 (31, 4) 15 (8±90) 3 32 28 (7) (21±40) 17.5 (12±30)
± ± ± ± <0.001 ±
± ±4.0 to 2.0 ± ± 3.6±10.0 0±5
(31, 5) (9±65) (6) (10±31) (11±26)
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The mean leak pressure achieved with the laryngeal tube (28 cm H2O) was signi®cantly greater than that for the classic LMA (21 cm H2O) (P<0.001; 95% CI 3.6±10.0 cm H2O; Table 2). Complications during anaesthesia were similar between the groups (Table 3). The main complications were leak of air around the device with the classic LMA and temporary airway obstruction with the laryngeal tube. In three patients allocated the laryngeal tube, manipulations were required to maintain a clear airway (15 manipulations in total). In one patient the laryngeal tube had to be removed and replaced with a classic LMA. Ventilation was rated as good in 25 patients, fair in 11, and failed in no patient with the classic LMA. With the laryngeal tube, ventilation was rated as good in 23, fair in 11 and failed in two (with one excluded at the insertion stage). There was no signi®cant difference in ef®cacy of ventilation between the groups.
The median peak airway pressure for the laryngeal tube (17.5 cm H2O) was greater than that for the classic LMA (16 cm H2O) (95% CI 0±5 cm H2O).
Comparison of laryngeal tube with classic LMA
Table 3 The number of patients in whom complications occurred during induction, maintenance, and emergence, and up to 24 h after operation. Severity of complications are shown as (mild/moderate/severe) Classic LMA (n=36) Induction of anaesthesia Bleeding Hiccups Hypoxia Total (one or more problems) Maintenance of anaesthesia Temporary loss of airway Excessive gas leak around the device `Blue' tongue Coughing or hiccups Total (one or more problems) Emergence from anaesthesia Excessive secretion Laryngospasm Desaturation Coughing or gagging Blood on the removed device Total (one or more problems) In the recovery room Sore throat Dysphagia Dysphonia Neck pain Numb mouth Total (one or more problems) 24 h after operation Sore throat Dysphagia Dysphonia Blocked ear Numb mouth Total (one or more problems)
Laryngeal tube (n=35)
1 1 0 2
0 0 1 1
0 4 1 0 5
3 2 2 2 7
0 1 1 4 1 4
4 0 1 3 1 6
9 5 1 1 1 11
(9/0/0) (4/1/0) (1/0/0) (1/0/0) (1/0/0)
7 4 2 0 0 7
(5/2/0) (4/0/0) (1/1/0) (0/0/0) (0/0/0)
11 5 1 0 1 11
(9/2/0) (5/0/0) (1/0/0)
12 6 2 2 0 12
(10/2/0) (6/0/0) (2/0/0)
(1/0/0)
(0/0/0)
who were breathing spontaneously. They found the laryngeal tube virtually impossible to use, with 25 of 27 uses being abandoned. The reason for the high failure rate in their report is not clear. The use of a prototype is a possible explanation, but it is possible that there were technical problems,15 since in patients in whom ventilation was controlled, placement of, and ventilation through, the laryngeal tube was often unsatisfactory in their study,3 but almost always successful in other reports.1 2 5 13 In the current study, we found the laryngeal tube was effective for controlled ventilation and encountered no problems when the patient progressed from controlled to spontaneous ventilation. Miller stated that he has found that the success rate of adequate ventilation through the new laryngeal tube is much higher than that for the prototype (Miller, personal communication, 2002). Although the ef®cacy of the devices was statistically equivalent there were two failures in the laryngeal tube group which were `salvaged' by use of the classic LMA. No failures occurred in the classic LMA group. Sub-optimal ventilation with classic LMA occurred most frequently because of an imperfect seal, and with the laryngeal tube because of obstruction. This drawback of the classic LMA (frequent leak) may be less with the LMA ProSealÔ. After completion of this study, Brimacombe and colleagues16 reported a study comparing the ef®cacy of the laryngeal tube with the ProSealÔ. They found that the air leak pressures were similar between the two devices, whereas expired tidal volumes were larger, the end-tidal carbon dioxide concentration was less and the incidence of airway obstruction during anaesthesia was less with the ProSealÔ.16 However, these authors used a previous version of the laryngeal tube, so it is not known how the new laryngeal tube performs compared with the ProSealÔ. One concern with the use of the laryngeal tube was that the device might not be tolerated by the patient during emergence from anaesthesia, because of its relatively large proximal cuff. However, as with the classic LMA, the laryngeal tube could be left in place until the patient had regained consciousness and opened the mouth to command, with no complications in most patients. Another concern was pressure damage to the oropharynx.17 However, the incidence and extent of sore throat, dysphagia, dysphonia, or numb mouth were similar. For example, the incidence of sore throat with the use of the laryngeal tube is similar to that reported after the classic LMA.18 19 Nevertheless, we detected apparent ischaemic changes to the tongue in two of 36 patients in whom the laryngeal tube was used. In these patients, no ischaemic changes were observed after de¯ating the cuffs. Two of 18 laryngeal tubes broke during the study. One proximal cuff tore on teeth and one returned from sterilization with the proximal cuff ruptured. It will require more widespread use of the device to determine if there is a problem with durability.
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required a greater airway peak pressure during anaesthesia. The greater peak airway pressure with the laryngeal tube could be because the laryngeal tube is narrower and has smaller distal apertures, which will increase the resistance. The laryngeal tube could also be placed in a suboptimal position and cause partial obstruction of the airway. The classic LMA is designed to occupy the hypopharynx so that, provided an appropriate size is chosen, the device is unlikely to be inserted too deeply. In contrast, the laryngeal tube can potentially be inserted too deeply so that its distal apertures face the hypopharyngeal wall, rather than the laryngeal inlet. This would lead to airway obstruction or ventilation via the side holes of the device. The incidence of malposition is not known, since the position has not been studied using a ®breoptic endoscope. The clinical relevance of the greater airway pressure with the laryngeal tube is unclear, but in our patients, we found no apparent problems. Nevertheless, high resistance in the airway would increase the work of breathing during spontaneous ventilation so that the laryngeal tube would not be as suitable as the classic LMA during spontaneous breathing. Miller, Youkhana and Pearce3 compared the classic LMA with a prototype laryngeal tube in anaesthetized patients
Cook et al.
In summary, the laryngeal tube allowed a greater pressure for controlled ventilation compared with the classic LMA, but peak airway pressure was greater and more manipulations were required during maintenance of anaesthesia.
Acknowledgement We thank VBM, Medizintechnik, Germany for donation of the laryngeal tubes.
References
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1 Asai T, Kawashima A, Hidaka I, Kawachi S. The laryngeal tube compared with the laryngeal mask: insertion, gas leak pressure and gastric insuf¯ation. Br J Anaesth 2002; 89: 729±32 2 Ocker H, Wenzel V, Schmucker P, Steinfath M, DoÈrges V. A comparison of the laryngeal tube with the laryngeal mask airway during routine surgical procedures. Anesth Analg 2002; 95: 1094± 5 3 Miller DM, Youkhana I, Pearce AC. The laryngeal mask and VBM laryngeal tube compared during spontaneous ventilation. A pilot study. Eur J Anaesthesiol 2001; 18: 593±8 4 Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict dif®cult tracheal intubation: a prospective study. Can Anaesth Soc J 1985; 32: 429±34 5 Samsoon GLT, Young JRB. Dif®cult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487±90 6 Asai T, Murao K, Shingu K. Ef®cacy of the laryngeal tube during intermittent positive pressure ventilation. Anaesthesia 2000; 55: 1099±102 7 Brimacombe JR, Brain AIJ, Berry AM. The Laryngeal Mask Instruction Manual for Anaesthesia. Henly-on-Thames, UK: Intavent Research Ltd, 1999
8 Asai T, Brimacombe J. Cuff volume and size selection with the laryngeal mask. Anaesthesia 2000; 55: 1179±84 9 Asai T, Morris S. The laryngeal mask airway: its features, effects and role. Can J Anaesth 1994; 41: 930±60 10 Armitage P, Berry G. Statistical Methods in Medical Research, 3rd Edn. Oxford: Blackwell Scienti®c Publications, 1994 11 Devitt JH, Wenstone R, Noel AG, O'Donnell MP. The laryngeal mask airway and positive-pressure ventilation. Anesthesiology 1994; 80: 550±5 12 Cook TM, Nolan JP, Verghese C, et al. A randomized crossover comparison of the Pro-Seal with the classic laryngeal mask airway in unparalysed anaesthetized patients. Br J Anaesth 2002; 88: 527±33 13 DoÈrge V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg 2000; 90: 1220±2 14 Asai T, Kawashima A, Hidaka I, Kawachi S. Laryngeal tube: its use for controlled ventilation. Masui (Japanese Journal of Anesthesiology) 2001; 50: 1340±1 15 Asai T, Hidaka I, Kubota T, Kawachi S. Ef®cacy of the laryngeal tube. Eur J Anaesthesiol 2002; 19: 305 16 Brimacbome J, Keller C, Brimacombe L. A comparison of the laryngeal mask airway ProSealÔ and the laryngeal tube airway in paralyzed anesthetized adult patients undergoing pressurecontrolled ventilation. Anesth Analg 2002; 95: 770±6 17 Mandal NG, Asai T. A new device has to be safe and reliable too. Anaesthesia 2001; 56: 382 18 Figuerdo E, Vivar-Diago M, Munoz-Blanco F. Laryngo-pharyngeal complaints after use of the laryngeal mask airway. Can J Anaesth 1999; 46: 220±5 19 Oczenski W, Krenn H, Dahaba AA, et al. Complications following the use of the Combitube, tracheal tube and laryngeal mask airway. Anaesthesia 1999; 54: 1161±5
DOI: 10.1093/bja/aeg192
Randomized comparison of laryngeal tube with classic laryngeal mask airway for anaesthesia with controlled ventilation T. M. Cook1*³, B. McCormick1 and T. Asai2 1
Royal United Hospital, Combe Park, Bath, UK. 2Assistant Professor, Kansai Medical University, 10±15 Fumizono-cho, Moriguchi City, Osaka 570±8507, Japan *Corresponding author
Methods. We randomly allocated 72 patients to receive either the laryngeal tube or an LMA, and compared adequacy of controlled ventilation during anaesthesia (good: clear airway without complications; fair; clear airway with complications or suboptimal airway; or failed), leak pressure and the incidence of postoperative complications. Results. Insertion was successful within 2 attempts in all 36 patients for the classic LMA and in 35 patients for the laryngeal tube. The mean leak pressure for the laryngeal tube (28 cm H2O) was signi®cantly greater than that for the classic LMA (21 cm H2O) (P<0.001; 95% CI 3.6±10.0 cm H2O). Ventilation was good in 25 cases, fair in 11, and failed in no patients with the classic laryngeal mask airway; and good in 23, fair in 11 and failed in two for the laryngeal tube. There was no signi®cant difference in adequacy of ventilation between the groups. The median peak airway pressure for the laryngeal tube (17.5 cm H2O) was greater than that for the classic LMA (16 cm H2O) (difference: 2 cm H2O; 95% CI 0±5 cm H2O). There was no signi®cant difference in the incidence and severity of the postoperative complications between the two groups. Conclusion. The laryngeal tube was as effective as the classic LMA during anaesthesia with controlled ventilation. There were similar operative and postoperative complications. Br J Anaesth 2003; 91: 373±8 Keywords: equipment, masks laryngeal; equipment, tubes laryngeal Accepted for publication: April 3, 2003
The laryngeal tube (VBM, Medizintechnik, Sulz, Germany) has been developed to secure a patent airway during either spontaneous breathing or controlled ventilation. It consists of an airway tube with a small balloon cuff attached at the tip (distal cuff), and a larger asymmetric balloon cuff at the middle part of the tube (proximal cuff; Fig. 1). The cuffs are in¯ated through a single pilot tube and balloon, through which cuff pressure can be monitored. There are two distal apertures in the tube between the two cuffs through which gas movement may take place. When the device is inserted, it lies along the length of the tongue and the distal tip is positioned in the hypopharynx. The proximal cuff provides a seal in the upper pharynx and the distal cuff seals the oesophageal inlet. There are three black lines on the tube near a standard 15-mm connector, which indicate adequate
depth of insertion when aligned with the teeth. The device is made of silicone and is re-usable, after sterilization in an autoclave, up to 50 times. There are ®ve sizes, suitable for neonates up to large adults. Since its introduction into clinical practice, the design of the laryngeal tube has been modi®ed on a few occasions: the prototype had two pilot tubes whereas the current device has one; a softer silicone has been used for the tip of the device (in the distal cuff) to reduce oropharyngeal injury; the distal aperture consists of two ori®ces (instead of one in the prototype); there is an indentation of the proximal cuff ²
LMAâ is the property of Intavent Limited. Declaration of interest. Dr Cook has received an honorarium from Intavent Limited. ³
Ó The Board of Management and Trustees of the British Journal of Anaesthesia 2003
Downloaded from http://bja.oxfordjournals.org/ at State Univ NY at Stony Brook on October 30, 2014
Background. Only a prototype laryngeal tube has been compared with the classic LMA² for brief periods of anaesthesia. We compared the new laryngeal tube (which had several improvements in design) with the classic LMA.
Cook et al.
Standard anaesthesia monitors were attached before induction of anaesthesia. The patient's head was supported on a ®rm pillow. After preoxygenation, anaesthesia was induced with a target controlled infusion of i.v. propofol set to give a predicted plasma concentration of 4±7 mg ml±1, and fentanyl 1 mg kg±1. Neuromuscular block was with rocuronium 0.6±1.0 mg kg±1, con®rmed using a peripheral nerve stimulator (train-of-four count=0) before airway manipulation. Anaesthesia was maintained with a targetcontrolled infusion of propofol. The patients were then allocated randomly to one of two groups, in which the laryngeal tube or the classic LMA was speci®ed for airway management. Randomization was by 72 sequentially numbered, sealed opaque envelopes containing equal numbers of the names of either of the two devices.
around the second distal ori®ce, and two side holes are added near the distal ori®ce. The laryngeal tube can be used as an alternative to the classic LMA during maintenance of anaesthesia. There have been three studies comparing the ef®cacy of the laryngeal tube with the classic LMA.1±3 One study showed that the success rates of insertion was similar in the two groups, and the laryngeal tube provided a better seal than the classic LMA.1 In a second study,2 arterial blood gas analysis obtained 10 min after insertion of the test device showed that the laryngeal tube was as effective as the classic LMA. However, in the third report,3 the study was stopped because of a high failure rate with the laryngeal tube. In all studies, prototype laryngeal tubes were used. There has been no study comparing the current type of the laryngeal tube with other airway devices, such as the classic LMA, and no studies comparing these two devices during the entire course of anaesthesia. Our aim was to compare the ef®cacy of the laryngeal tube with that of the classic LMA in paralysed patients during the entire course of anaesthesia, and to compare the sealing effects of the two devices.
Methods The local research ethics committee approved the study and all patients gave written informed consent. We studied 72 adult patients (ASA I or II) undergoing elective surgery in the supine or lithotomy position, in whom neuromuscular block was part of the anaesthetic technique and the use of the classic LMA was appropriate. Patients were excluded if they had any diseases of the neck, upper respiratory or upper alimentary tract, or if they were at risk of pulmonary aspiration of gastric contents. The view of the oropharynx at opening the mouth was scored according to Mallampati and colleagues4 as modi®ed by Samsoon and Young.5
The laryngeal tube was inserted according to the manufacturer's instructions. Brie¯y, before insertion, cuffs were de¯ated and a water-soluble lubricant (KY jelly) was applied to the cuffs. The patient's head was extended on the neck (`snif®ng position'). The tip of the laryngeal tube was placed against the hard palate behind the upper incisors and the device was slid down into the centre of the mouth until resistance was felt or the second bold black line on the tube had just passed between upper and lower teeth. The cuffs were in¯ated using a cuff in¯ator (VBM, Germany) until the intracuff pressure reached 80±90 cm H2O. The pressure was then reduced to 60±70 cm H2O.6 A size 3 was used for patients less than 155 cm, a size 4 for those between 155 cm and 180 cm, and a size 5 for those >180 cm in height.6 The classic LMA was inserted according to the manufacturer's instruction manual.7 A size 4 was used in females and a size 5 mask for males.8 The back of the cuff was lubricated with KY jelly. The cuff was in¯ated using the same cuff in¯ator until the intracuff pressure reached 60±70 cm H2O.7 In both groups, the breathing system was connected to the device. We assessed adequacy of ventilation by gently squeezing the reservoir bag, observing the presence of endtidal carbon dioxide waveforms and chest movement. If it was not possible to ventilate the lungs, the following airway manoeuvres were allowed: chin lift, jaw thrust, head extension, or ¯exion on the neck. In the case of the laryngeal tube, the position was also allowed to be adjusted by gently pushing or pulling the device (whereas no such manoeuvre was allowed for the classic LMA). After any manoeuvre, adequacy of ventilation was re-assessed. If it was not possible to insert the device or ventilate through it, one more attempt at insertion was allowed. If placement had failed after two attempts, the study was abandoned and the airway maintained either through a classic LMA or such other airway device as suitable. Time for insertion of the airway (from time of picking up the device to attaching it to the breathing system after
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Insertion of the device
Fig 1 The laryngeal tube (VBM, Germany).
Comparison of laryngeal tube with classic LMA
in¯ation of the cuff) was measured in patients in whom it was possible to ventilate the lungs. To measure the seal pressure, fresh gas was insuf¯ated at 5 litre min±1, the spill valve occluded and we recorded the minimum airway pressure at which gas could either be heard leaking around the airway device or the airway pressure plateaued. Peak airway pressure was not allowed to exceed 40 cm H2O.
Maintenance of anaesthesia
Removal of the device At the end of the operation, anaesthetic agents were discontinued while the device was left in place. The device was removed after the patient regained consciousness spontaneously and responded to verbal command to open the mouth. However, if necessary (e.g. airway obstruction or retching occurred), it could be removed before this point. Before removal, the cuffs of the laryngeal tube were de¯ated, whereas the cuff of the classic LMA was not (in accordance with the manufacturers' recommendations7). At removal, the presence or absence of secretions interfering with airway management and of blood on the device was recorded. Complications, were de®ned, a priori, with the use of the devices during induction, maintenance, and emergence.
Postoperative period Within 2 h and again at 24 h after surgery, each patient was questioned to determine the following complications: sore throat (constant pain, independent of swallowing), dysphagia (dif®culty or pain with swallowing), sore jaw, dysphonia (dif®culty or pain with speaking), numbness of the tongue or the oropharynx, blocked or painful ears, reduced hearing, or neck pain. Each complication was graded as: none, mild, moderate or severe. Those patients discharged from hospital within 24 h after surgery were followed-up by telephone.
The primary aim of the study was to compare the success rates of two airway devices in establishing a patent airway allowing ventilation without complications. The secondary aim was to compare the leak pressures between two groups. We calculated the number of patients required for the study based on these two factors. The rate of the classic LMA providing a patent airway is 95±100%.9 Our hypothesis was that there would be no difference in the ef®cacy of the two devices in terms of ventilation during anaesthesia, with a clinically important difference being 10%. Seventy-two patients would be required to assess this hypothesis, with a power of 80% and a one-sided 95% con®dence interval (CI), using an equivalence test.10 The mean airway pressure at which gas leaks around the classic laryngeal mask airway ranges from 18 to 20 cm H2O (SD ~5 cm H2O).11 12 We considered that an increase in leak pressure of 30% would be clinically signi®cant. Twenty-two patients would be required to detect this difference with a power of 80%. Therefore, we studied 72 patients. The c2-test was used to compare the ef®cacies of the two devices: good (optimal ventilation without complications during anaesthesia), fair (optimal ventilation with complications or suboptimal ventilation), and failure (failed insertion or abandonment of the use). Plots of normal scores showed that the data for leak pressures were normally distributed. Therefore, the Student's t-test was used to compare the leak pressures between two groups. For additional information, we also applied the third hypothesis test (c2-test) to compare the incidence of postoperative complications between groups. For this analysis, the number of patients was counted for no, mild, moderate or severe complication. The data for 0±2 h and 24 h after surgery were pooled for analysis and for each patient, with the severest score recorded. P<0.05 was considered signi®cant. We noticed after the start of the study that there might be a difference in the peak airway pressures during anaesthesia between the laryngeal tube and classic LMA. Therefore, the con®dence interval was used to compare this factor. The data for insertion time and for the peak pressure were not normally distributed. Therefore, the 95% CIs were calculated for the median difference of insertion time, the median difference of peak airway pressure, and the mean difference of the leak pressures, between the two devices.
Results Thirty-six patients were studied in each group. Patient characteristics, size of the device used, and duration of anaesthesia, were similar in the two groups (Table 1).
Insertion of the device There was one failure to establish an airway with the laryngeal tube and none with the classic LMA after two
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After securing the device, controlled ventilation in oxygen and air was started with a tidal volume of 7 ml kg±1 and an inspiratory/expiratory ratio of 1:2. The respiratory rate was adjusted to maintain the end-tidal carbon dioxide concentration in the normal range. Ventilation was judged to be optimal if the following four tests were passed: (i) adequate chest movement; (ii) an expired tidal volume of 7 ml kg±1; (iii) stable oxygenation; and (iv) `square wave' capnography. If airway obstruction occurred during anaesthesia, manoeuvring the position of the device or the patient's head and neck, or removal and reinsertion of the device were allowed. The number of manipulations of each device during insertion and maintenance of anaesthesia was recorded for each device.
Statistical analysis
Cook et al.
attempts at insertion (Table 2). Two attempts were required in four patients with the laryngeal tube and in ®ve with the classic LMA. Insertion of the laryngeal tube required manipulations in three patients, but the time taken for insertion was similar for the two groups (Table 2). There were few complications of insertion in either group (Table 3). In the patient in whom insertion of the laryngeal tube failed, there was temporary hypoxia and it was removed. The classic LMA provided a clear airway in this patient.
Maintenance of anaesthesia
Table 1 Patient characteristics, the size of the device used, and duration of anaesthesia. Data are presented as number of patients or mean (SD) for height and weight, mean (range) for age
Sex (M/F) Age (yr) Height (cm) Weight (kg) BMI (kg m±2) View of the oropharynx Mallampati class4 5 1/2/3/4 Size of the device used Size 3/4/5 Duration of anaesthesia (min)
Classic LMA (n=36)
Laryngeal tube (n=36)
21/15 52 (22±84) 171 (10) 78 (14) 27 (4) (21±38)
18/18 56 (22±82) 167 (10) 75 (15) 27 (5) (19±43)
13/18/4/1
15/15/5/1
2/16/18 46 (27) (15±142)
2/30/4 49 (24) (15±120)
Removal of the device The airways were equally well tolerated during emergence from anaesthesia: there was no need to remove the airway before the patient regained consciousness with either device. Complications during emergence and recovery from anaesthesia were few and mostly minor (Table 3). One patient in the classic LMA group developed laryngospasm, stridor and mild desaturation. One patient in the laryngeal tube group developed airway obstruction and mild desaturation. On removal, blood was present on one device in each group (Table 3).
Postoperative period Postoperative complications that could be attributed to the airway device were observed in one-third of patients in each group (Table 3), and there was no signi®cant difference in incidence and severity between the groups.
Discussion We have shown that the laryngeal tube is as effective as the classic LMA at providing a patent airway during controlled ventilation of the lungs, and that the laryngeal tube gave a signi®cantly greater sealing pressure than the classic LMA. The success rate of obtaining a patent airway through the laryngeal tube was high (97%). This result supports previous reports, where the success rate was 94±100% immediately after insertion of the device.1 2 6 13 14 The laryngeal tube provided a patent airway as frequently as the classic LMA, not only during induction of anaesthesia, but also during maintenance of anaesthesia. The airway seal pressure achieved with the laryngeal tube was signi®cantly greater than that with the classic LMA (Table 2), which also supports a previous study.1 2 In this regard, the laryngeal tube may be more useful than the classic LMA for controlled ventilation. The increased seal pressure of the laryngeal tube is achieved with two minor costs: the laryngeal tube required more re-adjustment because of airway obstruction and
Table 2 Success rate of, and time for, insertion of the device, the number of patients in whom manipulation of the device was required to obtain a clear airway, and in whom ventilation was optimal (see details in the text). Data presented as mean (SD) (range) for the leak pressure; median (range) for the insertion time and peak airway pressure
Successful ventilation (1st, 2nd attempt) Time for insertion (s) Manipulations Optimal ventilation Leak pressure (cm H2O) Peak airway pressure (cm H2O)
Classic LMA (n=36)
Laryngeal tube (n=36)
P-value
95% CI
36 15 0 29 21 16
35 (31, 4) 15 (8±90) 3 32 28 (7) (21±40) 17.5 (12±30)
± ± ± ± <0.001 ±
± ±4.0 to 2.0 ± ± 3.6±10.0 0±5
(31, 5) (9±65) (6) (10±31) (11±26)
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The mean leak pressure achieved with the laryngeal tube (28 cm H2O) was signi®cantly greater than that for the classic LMA (21 cm H2O) (P<0.001; 95% CI 3.6±10.0 cm H2O; Table 2). Complications during anaesthesia were similar between the groups (Table 3). The main complications were leak of air around the device with the classic LMA and temporary airway obstruction with the laryngeal tube. In three patients allocated the laryngeal tube, manipulations were required to maintain a clear airway (15 manipulations in total). In one patient the laryngeal tube had to be removed and replaced with a classic LMA. Ventilation was rated as good in 25 patients, fair in 11, and failed in no patient with the classic LMA. With the laryngeal tube, ventilation was rated as good in 23, fair in 11 and failed in two (with one excluded at the insertion stage). There was no signi®cant difference in ef®cacy of ventilation between the groups.
The median peak airway pressure for the laryngeal tube (17.5 cm H2O) was greater than that for the classic LMA (16 cm H2O) (95% CI 0±5 cm H2O).
Comparison of laryngeal tube with classic LMA
Table 3 The number of patients in whom complications occurred during induction, maintenance, and emergence, and up to 24 h after operation. Severity of complications are shown as (mild/moderate/severe) Classic LMA (n=36) Induction of anaesthesia Bleeding Hiccups Hypoxia Total (one or more problems) Maintenance of anaesthesia Temporary loss of airway Excessive gas leak around the device `Blue' tongue Coughing or hiccups Total (one or more problems) Emergence from anaesthesia Excessive secretion Laryngospasm Desaturation Coughing or gagging Blood on the removed device Total (one or more problems) In the recovery room Sore throat Dysphagia Dysphonia Neck pain Numb mouth Total (one or more problems) 24 h after operation Sore throat Dysphagia Dysphonia Blocked ear Numb mouth Total (one or more problems)
Laryngeal tube (n=35)
1 1 0 2
0 0 1 1
0 4 1 0 5
3 2 2 2 7
0 1 1 4 1 4
4 0 1 3 1 6
9 5 1 1 1 11
(9/0/0) (4/1/0) (1/0/0) (1/0/0) (1/0/0)
7 4 2 0 0 7
(5/2/0) (4/0/0) (1/1/0) (0/0/0) (0/0/0)
11 5 1 0 1 11
(9/2/0) (5/0/0) (1/0/0)
12 6 2 2 0 12
(10/2/0) (6/0/0) (2/0/0)
(1/0/0)
(0/0/0)
who were breathing spontaneously. They found the laryngeal tube virtually impossible to use, with 25 of 27 uses being abandoned. The reason for the high failure rate in their report is not clear. The use of a prototype is a possible explanation, but it is possible that there were technical problems,15 since in patients in whom ventilation was controlled, placement of, and ventilation through, the laryngeal tube was often unsatisfactory in their study,3 but almost always successful in other reports.1 2 5 13 In the current study, we found the laryngeal tube was effective for controlled ventilation and encountered no problems when the patient progressed from controlled to spontaneous ventilation. Miller stated that he has found that the success rate of adequate ventilation through the new laryngeal tube is much higher than that for the prototype (Miller, personal communication, 2002). Although the ef®cacy of the devices was statistically equivalent there were two failures in the laryngeal tube group which were `salvaged' by use of the classic LMA. No failures occurred in the classic LMA group. Sub-optimal ventilation with classic LMA occurred most frequently because of an imperfect seal, and with the laryngeal tube because of obstruction. This drawback of the classic LMA (frequent leak) may be less with the LMA ProSealÔ. After completion of this study, Brimacombe and colleagues16 reported a study comparing the ef®cacy of the laryngeal tube with the ProSealÔ. They found that the air leak pressures were similar between the two devices, whereas expired tidal volumes were larger, the end-tidal carbon dioxide concentration was less and the incidence of airway obstruction during anaesthesia was less with the ProSealÔ.16 However, these authors used a previous version of the laryngeal tube, so it is not known how the new laryngeal tube performs compared with the ProSealÔ. One concern with the use of the laryngeal tube was that the device might not be tolerated by the patient during emergence from anaesthesia, because of its relatively large proximal cuff. However, as with the classic LMA, the laryngeal tube could be left in place until the patient had regained consciousness and opened the mouth to command, with no complications in most patients. Another concern was pressure damage to the oropharynx.17 However, the incidence and extent of sore throat, dysphagia, dysphonia, or numb mouth were similar. For example, the incidence of sore throat with the use of the laryngeal tube is similar to that reported after the classic LMA.18 19 Nevertheless, we detected apparent ischaemic changes to the tongue in two of 36 patients in whom the laryngeal tube was used. In these patients, no ischaemic changes were observed after de¯ating the cuffs. Two of 18 laryngeal tubes broke during the study. One proximal cuff tore on teeth and one returned from sterilization with the proximal cuff ruptured. It will require more widespread use of the device to determine if there is a problem with durability.
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required a greater airway peak pressure during anaesthesia. The greater peak airway pressure with the laryngeal tube could be because the laryngeal tube is narrower and has smaller distal apertures, which will increase the resistance. The laryngeal tube could also be placed in a suboptimal position and cause partial obstruction of the airway. The classic LMA is designed to occupy the hypopharynx so that, provided an appropriate size is chosen, the device is unlikely to be inserted too deeply. In contrast, the laryngeal tube can potentially be inserted too deeply so that its distal apertures face the hypopharyngeal wall, rather than the laryngeal inlet. This would lead to airway obstruction or ventilation via the side holes of the device. The incidence of malposition is not known, since the position has not been studied using a ®breoptic endoscope. The clinical relevance of the greater airway pressure with the laryngeal tube is unclear, but in our patients, we found no apparent problems. Nevertheless, high resistance in the airway would increase the work of breathing during spontaneous ventilation so that the laryngeal tube would not be as suitable as the classic LMA during spontaneous breathing. Miller, Youkhana and Pearce3 compared the classic LMA with a prototype laryngeal tube in anaesthetized patients
Cook et al.
In summary, the laryngeal tube allowed a greater pressure for controlled ventilation compared with the classic LMA, but peak airway pressure was greater and more manipulations were required during maintenance of anaesthesia.
Acknowledgement We thank VBM, Medizintechnik, Germany for donation of the laryngeal tubes.
References
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8 Asai T, Brimacombe J. Cuff volume and size selection with the laryngeal mask. Anaesthesia 2000; 55: 1179±84 9 Asai T, Morris S. The laryngeal mask airway: its features, effects and role. Can J Anaesth 1994; 41: 930±60 10 Armitage P, Berry G. Statistical Methods in Medical Research, 3rd Edn. Oxford: Blackwell Scienti®c Publications, 1994 11 Devitt JH, Wenstone R, Noel AG, O'Donnell MP. The laryngeal mask airway and positive-pressure ventilation. Anesthesiology 1994; 80: 550±5 12 Cook TM, Nolan JP, Verghese C, et al. A randomized crossover comparison of the Pro-Seal with the classic laryngeal mask airway in unparalysed anaesthetized patients. Br J Anaesth 2002; 88: 527±33 13 DoÈrge V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg 2000; 90: 1220±2 14 Asai T, Kawashima A, Hidaka I, Kawachi S. Laryngeal tube: its use for controlled ventilation. Masui (Japanese Journal of Anesthesiology) 2001; 50: 1340±1 15 Asai T, Hidaka I, Kubota T, Kawachi S. Ef®cacy of the laryngeal tube. Eur J Anaesthesiol 2002; 19: 305 16 Brimacbome J, Keller C, Brimacombe L. A comparison of the laryngeal mask airway ProSealÔ and the laryngeal tube airway in paralyzed anesthetized adult patients undergoing pressurecontrolled ventilation. Anesth Analg 2002; 95: 770±6 17 Mandal NG, Asai T. A new device has to be safe and reliable too. Anaesthesia 2001; 56: 382 18 Figuerdo E, Vivar-Diago M, Munoz-Blanco F. Laryngo-pharyngeal complaints after use of the laryngeal mask airway. Can J Anaesth 1999; 46: 220±5 19 Oczenski W, Krenn H, Dahaba AA, et al. Complications following the use of the Combitube, tracheal tube and laryngeal mask airway. Anaesthesia 1999; 54: 1161±5